Microfluidic channel device with array of drive electrodes

ABSTRACT

Technologies are generally described for microfluidic channel devices. Some example devices may include a substrate having a substrate surface, with an array of drive electrode assemblies disposed upon the substrate surface. The drive electrode assemblies may be arranged along a path. Each drive electrode assembly may include one or more of a drive electrode layer, a dielectric layer and/or a stationary phase layer. The device may further include a plate including a plate surface. The device may further include a reference electrode configured on the plate surface to face the stationary phase layer of the drive electrode assemblies and separated from the substrate surface by a distance. The device may further include a voltage source effective to output a voltage potential, the voltage source configured in communication with the drive electrode assembly and the reference electrode. The device may further include an electrode selector effective to control the voltage source.

BACKGROUND

Unless otherwise expressly indicated herein, none of the materialpresented in this section is prior art to the claims of this applicationand is not admitted to be prior art by having been included herein.

Microchemical reactors may be used as platforms for chemical discoveryand synthesis. Many reactors rely on microfluidic channel and“lab-on-a-chip” concepts. Fluids are commonly transported through suchdevices by capillary action, micro-pumps or electro-kinetic actuation.In synthetic chemistry, separation, isolation and identification ofreaction product(s) are often accomplished by various methods ofchromatography ranging from simple paper chromatography and thin layerchromatography (referred to as “TLC”) to advanced high pressure liquidchromatography (referred to as “HPLC”).

BRIEF DESCRIPTION OF THE FIGURES

The foregoing and other features of this disclosure will become morefully apparent from the following description and appended claims takenin conjunction with the accompanying drawings. Understanding that thesedrawings depict only some embodiments in accordance with the disclosureand are therefore not to be considered limiting of its scope, thedisclosure will be described with additional specificity and detail byreference to the accompanying drawings in which:

FIG. 1 is a side cross-sectional schematic view of a microfluidicchannel device;

FIGS. 2, 3 and 4A-E are schematic illustrations of stages in theconstruction of a microfluidic channel device;

FIG. 5 is a perspective view of a microfluidic channel device;

FIG. 6A is side cross-sectional schematic view of a planarmicrochromatograph incorporating a microfluidic channel device;

FIG. 6B is side cross-sectional schematic view of a planarmicrochromatograph incorporating a microfluidic channel device;

FIG. 6C is a top plan schematic view of a planar microchromatographincorporating a microfluidic channel device;

FIG. 7 is a schematic illustration of an analytical system; and

FIG. 8 is a block diagram illustrating an example computer device thatis arranged to control a microfluidic channel device;

all arranged according to at least some embodiments described herein.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part thereof. In the drawings,similar symbols typically identify similar components unless contextindicates otherwise. The illustrative embodiments described in thedetailed description, drawings and claims are not meant to be limiting.Other embodiments may be utilized and other changes may be made withoutdeparting from the spirit or scope of the subject matter presentedherein. It will be readily understood that the aspects of the presentdisclosure as generally described herein and as illustrated in theaccompanying figures can be arranged, substituted, combined, separatedand/or designed in a wide variety of different configurations all ofwhich are explicitly contemplated herein.

This disclosure is generally drawn, inter alia, to apparatuses, systems,devices and methods relating to a microfluidic channel device forseparating and/or analyzing small volumes of chemical products.

Briefly stated, technologies are generally described for microfluidicchannel devices. Some example devices may include a substrate having asubstrate surface, with an array of drive electrode assemblies disposedupon the substrate surface. The drive electrode assemblies may bearranged along a path. Each drive electrode assembly may include one ormore of a drive electrode layer, a dielectric layer and/or a stationaryphase layer. The device may further include a plate including a platesurface. The device may further include a reference electrode configuredon the plate surface to face the stationary phase layer of the driveelectrode assemblies and separated from the substrate surface by adistance. The device may further include a voltage source effective tooutput a voltage potential, the voltage source configured incommunication with the drive electrode assembly and the referenceelectrode. The device may further include an electrode selectoreffective to control the voltage source.

As discussed in more detail below, a microfluidic channel device mayinclude a planar array of drive electrodes within a microfluidicchannel, where the planar array of drive electrodes are configured toproduce an electrowetting effect. A voltage potential difference may beapplied in a desired sequence to achieve liquid droplet movement alongthe length of the microfluidic channel. The microfluidic channel devicedescribed herein may be adapted for use in a stand-alonemicro-chromatograph device or system. In some examples, the microfluidicchannel device may be integrated into a microfluidic lab-on-a chipdevice or system.

FIG. 1 is a side cross-sectional schematic view of a microfluidicchannel device in accordance with at least some embodiments herein. Amicrofluidic channel device 10 may be used in a microfluidic planarchromatograph such as that illustrated in FIGS. 6A-C. Microfluidicchannel device 10 includes a plate 11, a reference electrode 12configured in contact with plate 11 and including a surface 16, asubstrate 13 including a surface 14, an array of drive electrodeassemblies 15 configured in adherent contact with surface 14, and aheater 9.

In some examples, microfluidic channel device 10 includes plate 11 butdoes not include reference electrode 12. In other examples, microfluidicchannel device includes reference electrode 12 but does not includeplate 11. Surface 16 of reference electrode 12 may be separated fromsurface 14 of substrate 13 by a predetermined distance 17 defining theheight dimension of microfluidic channel 18. A size of distance 17 maybe adjusted by moving reference electrode 12 and substrate 13. Forexample, if a reaction changes a volume of an analyte (discussed in moredetail below) a size of distance 17 may be adjusted accordingly. Channel18 may define any type of cross-sectional shape. In some examples,channel 18 may define a cross-section that is square, rectangular,elliptical, racetrack, oval, diamond, hexagonal, circular, andconcentric circles, etc. In some examples, reference electrode 12 anddrive electrode assemblies 15 extend parallel to one another and havethe same cross-sectional shape.

The height and width dimensions of microfluidic channel 18 may beconfigured to accommodate a droplet 60 containing analytes forseparation. For example channel 18 may have a width of about 10 μm toabout 5 mm; a height of about 1 μm to about 5 mm; and a length of about0.5 mm to about 50 mm. An array of spaced-apart drive electrodeassemblies 15 may be disposed upon surface 14 of substrate 13 to definethe length or longitudinal direction of microfluidic channel 18. In someexamples, each drive electrode assembly 15 may have a height of about1.01 μm to about 2 mm. Gap spaces 19 between each drive electrodeassembly 15 may be arranged substantially co-planar with the driveelectrode assemblies 15. In some examples, gap spaces 19 may extendabout 0.5 μm to about 50 μm, In some examples, gap spaces 19 may befiled with an electrically insulating material such as an opticallytranslucent material. Each drive electrode assembly 15 may be configuredadjacent to at least one of gap spaces 19. Each drive electrode 15 mayinclude a drive electrode layer 20, an intermediate dielectric layer 21,and a stationary phase layer 22. A surface 23 of stationary phase layer22 may be configured to face microfluidic channel 18 and referenceelectrode 12. A distance between surface 23 and surface 16 may beadjusted as desired for varying thicknesses in a single elution.

Plate 11 and substrate 13 may be fabricated from the same or differentchemically inert material(s), e.g., glass(es), ceramic(s), polymer(s),etc., combinations thereof, and the like. Representative glassesinclude, without limitation, silicates, borosilicates andaluminosilicates. Representative ceramics include, without limitation,Al₂O₃ in various purities, nitrides such as Si₃N₄, SiON and AlN.Representative polymers include, without limitation, polyacrylates,polystyrene, polycarbonate, polyamides, polyimides and epoxies.Substrate 13 may also include silicon with patterned oxide, nitride, orpolymer channels. Alternatively, microfluidic channel 18 may be etchedonto surface 14 of substrate 13.

In some examples, a fluid channel 18 may be formed on the surface ofsubstrate 13. As discussed above, channel 18 may be, in some examples,linear or circular in cross-section and may have branching points suchthat droplet 60 may be moved and turned through adjustment of voltages.The length of microfluidic channel 18 may be a function of the desiredresolution of an associated planar chromatograph Longer channels mayproduce higher resolutions. In examples including lab-on-a chiparchitectures, the length of microfluidic channel 18 may range fromabout 1 mm to about 10 cm and the width of the microfluidic channel 18may range from about 10 microns to about 5 mm.

As shown in FIG. 1, planar array of drive electrode assemblies 15 may bepatterned onto surface 14 of substrate 13. Various techniques may beused to create drive electrode assemblies 15. For example, driveelectrode layer 20 may be vapor-deposited as a thin film by evaporationor sputtering. Alternatively, drive electrode layer 20 may be depositedby any of several suitable electroplating techniques. Drive electrodelayer 20 may be patterned by photolithographic, lift off, etching orshadow mask methods. Drive electrode layer 20 may be fabricated from anysuitable metal. The selection of the metal may depend upon the abilityof the metal to satisfactorily adhere to dielectric layer 21, which maybe subsequently formed on the metal. The metal constituting the driveelectrode layer 20 need not be chemically inert since dielectric layer22 will isolate drive electrode layer 20 from the mobile phase and theanalytes Metals that may be used for providing drive electrode layer 20may include, without limitation, aluminium (Al), copper (Cu), gold (Au),nickel (Ni), silver (Ag), platinum (Pt), titanium (Ti) and their alloys.Depending upon the deposition method, in some examples, dimensions ofdrive electrode layer 20 may be: width—about 10 μm to about 5 mm;thickness—about 10 nm to about 1 μm; length—about 10 μm to about 1 mm.

Onto the surface of each metal electrode layer 20 may be an intermediatelayer 21 that can be implemented as a dielectric adhesion layer.Dielectric adhesion layer 21 may serve two purposes: as a dielectriclayer disposed between the mobile phase and each drive electrode layer20, and as a chemical adhesion layer disposed between each driveelectrode layer 20 and each stationary phase layer 22. The compositionand the thickness of dielectric adhesion layer 21 may be tailored asdesired to serve as a chemical linkage or physical bonding between driveelectrode layer 20 and each stationary phase layer 22 as well as aninsulator between the latter two layers. Various organic and/orinorganic materials may be utilized for the construction of dielectricadhesion layer 21. Representatives of such materials include organicpolymers such as polysilanes, polyacrylates and polyimides and inorganicmaterials such as oxides and nitrides. In some examples, the thicknessof dielectric adhesion layer 21 may range from about 1 nm to about 1000nm.

Stationary phase layer 22 may be formed from any of the materials thatare useful as the stationary phase in thin layer chromatography (TLC) orhigh performance liquid chromatography (HPLC). In some examples, athickness of stationary phase layer 22 may be about 1 μm to 1 mm. Arepresentative stationary phase layer can be fabricated from suchmaterials as, without limitation, functionalized silica particles,highly engineered gels, hydrogels, polymers such as polyacrylimide,nanoparticle assembles and porous particulate dispersions. The selectionof a specific material for stationary phase layer 22 may be based on thenature of the analytes to be separated. Various properties of theanalytes may be taken into consideration when choosing the material forstationary phase layer 22 including, without limitation, the polarity,charge and molecular size of the analytes. Depending upon the type ofseparation desired, stationary phase layer 22 may function in accordancewith any desired separation mechanism including, without limitation,normal or reverse phase configurations, binding affinity, ion exchangeor size exclusion. In some examples, different types of material may beused for stationary phase layers 22 in a single device 10. For example,a material of a first stationary phase layer 22 may be chosen based onsize exclusion and a material of a second stationary phase layer 22 maybe chosen based on binding affinity

Still referring to FIG. 1, a reference electrode 12 may be disposed uponthe surface of plate 11 in a configuration that faces surface 14 ofsubstrate 13. In some examples, and as shown in FIG. 1, referenceelectrode 12 may be provided as a single continuous layer disposed uponthe surface of plate 11 and shared by all planar-arrayed drive electrodeassemblies 15. In other examples, reference electrode 12 may comprise anarray of spaced-apart reference electrode units 12′ that may be disposedupon plate 11, each reference electrode 12′ facing a corresponding driveelectrode assembly 15. In some examples, a continuous referenceelectrode 12 may provide single fast elution whereas discontinuouselectrode units 12′ may allow branching into other channels and maycompensate for droplet shape changes during elution. For example, when adroplet goes through channel 18, analytes in the droplet may be elutedgradually. This can cause a surface tension change and/or acharge/polarity change on the droplet. A potential across referenceelectrode 12′ and the drive electrode 15 may be adjusted accordingly tocontrol the shape and, therefore, the movement of the droplet. Referenceelectrode 12 may be optically translucent. In some examples, both plate11 and reference electrode 12 may be optically translucent in order toallow the detection and/or identification of the separated analytes asdescribed in detail below.

Reference electrode 12 may be fabricated from a translucent conductormaterial such as indium tin oxide (ITO), tin oxide (SnO₂) or zinc oxide(ZnO). In some examples, the thickness of reference electrode 12 mayrange from about 100 nm to about 10 μm. Reference electrode 12 may beconfigured to establish an adjusting voltage potential acrossmicrofluidic channel 18, which can modify the contact angle and thesurface tension of sample droplet 60. For example, by changing theadjusting voltage potential, device 10 may move, deform,compress/elongate, confine and/or shape the sample droplet 60 introducedinto microfluidic channel 18. When sample droplet 60 is driven overstationary phase layer 22 of each drive electrode assembly 15 along thelength of microfluidic channel 18, various analytes may be removed fromsample droplet 60. Such analytes may diffuse within and be immobilizedon stationary phase layer 22. This diffusion may lead to polaritychanges in the analyte-depleted sample droplet. In order to maintain theelectrowetting-caused movement of the sample droplet, shape modificationof the droplet may be desirable as the sample droplet undergoes polaritychanges.

A microfluidic channel device in accordance with the disclosure mayinclude multiple microfluidic channels in communication with oneanother. Such a structure may provide for branching of a droplet tomultiple channels facilitating secondary elution and/or separation. Themicrofluidic channel may be filled with a surrounding medium. Aviscosity of the medium may be chosen to allow for introduction andequilibration. In some examples, the surrounding medium and the mobilephase may be immiscible. Any suitable pairing of organic and/or aqueoussolvents may be used for the surrounding medium and the mobile phase.For example, the surrounding medium and the mobile phase may beindependently hydrophobic, hydrophilic, aqueous, non-aqueous, polar ornon-polar. In some examples, the mobile phase may be oil-based and thesurrounding medium may be water.

An adjusting voltage between the drive electrode 20 having same droplet60 in proximity therewith and reference electrode 12 may be used inorder to allow the sample droplet to change shape and be displaced. Thismay allow droplet 60 to be moved along drive electrode 12 as a result ofthe electrowetting effect. When the sample droplet and the surroundingmedium have contrasting polarity, deformation of the droplet may occur.In these examples, the surface tension of the droplet may be adjusted.For example, when using hexane as the mobile phase and deionized (DI)water as the surrounding medium, surface tension of the droplet may beadjusted by the introduction of surfactants into the surrounding medium.In some examples, the mobile phase may be polar and the surroundingmedium may be ambient air. In some examples, the mobile phase may bepolar and the surrounding medium may be an evacuated cavity. In someexamples, the mobile phase may be non-polar and the surrounding mediummay be polar. Therefore, depending upon the nature of the analytes to beseparated, various chromatography methods may be utilized (as inconventional HPLC) in which the polarity contrasts between the mobilephase and the surrounding medium may be adjusted to achieve desiredseparation rates and resolution. Heater 9 may be arranged to provideheat to channel 18 and thereby adjust a viscosity of the mobile phase,and/or a binding affinity of the stationary phase. Again, referring toFIG. 1, reference electrode 12 and drive electrode layer 20 of eachdrive electrode assembly 15 may be in communication with an electrodeselector 25 via electrical connectors 24. Electrode selector 25 maycontrol voltage inputs, timings and durations to drive electrodeassembly 15 and reference electrode 12. In some examples, electrodeselector 25 may be controlled by a controller, a processor or a computer26.

FIGS. 2, 3 and 4A-E are schematic illustrations of stages in theconstruction of a microfluidic channel device in accordance with atleast some embodiments herein.

Referring to FIG. 2, surface 14 of substrate 13 may be patterned withdrive electrode layer 20. This patterning may be achieved byresist-based photolithography (e.g., positive or negative photoresist)and metals may be deposited on surface 14 via methods such assputtering, evaporation or electroplating. Chemical etching and resiststripping may also be used to form the pattern on the surface 14 of thesubstrate 13. Drive electrode layer 20 may be patterned on the surface14 of substrate 13 in any desired form. In some examples, driveelectrode layers 20 may be patterned as a linear array of electrode pads(e.g., square, rectangular, round, elliptical) or some other suitablegeometry. Each drive electrode layer may include an independentconductor trace 30 that is patterned on the surface 14 of substrate 13to the exterior portions of the microfluidic channel assembly tofacilitate external electrical connection.

Referring to FIG. 3, a layer of adhesive insulator material, i.e.,dielectric adhesion layer 21, may be deposited upon the surface of driveelectrode layer 20. The deposition on the adhesive dielectric layer 21can be accomplished by, for example, low temperature chemical vapordeposition of oxides or by spin, dip, screen print or vapor coating oforganics or polymers. Dielectric adhesion layer 21 may be deposited overthe entire surface of drive electrode layer 20 as shown in FIG. 3. Insome examples, the thickness of dielectric adhesion layer 21 may be in arange from about 1 nm to about 1000 nm.

Stationary phase layer 22 may be applied to or formed upon the surfaceof dielectric adhesion layer 21 to complete drive electrode assembly 15.Stationary phase layer 22 may enable one or more microfluidic channelsto have a chromatographic function. Stationary phase layer 22 may be ina range of thickness from about 10 nm to about 10 μm. In the mannerdescribed above, an example substrate assembly 35 may be produced.

Referring to FIGS. 4A-4E, starting with a monolithic slab 40 of selectedconstruction material as shown in FIG. 4A, planar-surfaced microfluidicchannel 18 can be formed therein by such microfabrication techniques aschemical etching, plasma/reactive ion dry etching, mechanical machining,electrical discharge machining, laser machining, molding, imprinting,lithographic patterning or any other suitable manufacturing technique.These example techniques may be utilized to provide plate 11 withmicrofluidic channel 18 in the configuration illustrated in FIG. 4B. Insome examples, the length of microfluidic channel 18 may be in a rangefrom about 1 mm to about 10 cm, the width of microfluidic channel 18 maybe in a range from about 10 μm to about 5 mm and the height, or depth,of microfluidic channel 18 may be in a range from about 10 μm to about 5mm.

As shown in FIG. 4C, reference electrode 12 may be deposited upon thesurface of plate 11 by vapor or sputter deposition methods. Referenceelectrode 12 may be in a range in thickness (depth) from about 1 nm toabout 1000 nm and may include a trace conductor 80 that is configured tothe exterior of the plate 11.

In FIG. 4D, an adhesive layer 45 may be applied to the non-channelledportions of plate 11. Various types of automatic fluid dispensingequipment may be used for the application of adhesive layer 45. In someexamples, the application of the adhesive layer may be carried out usinga robotic syringe adhesive dispenser. Plate 11 with adhesive 45 may thenbe inverted and bonded to substrate assembly 35 such that referenceelectrode 12 is configured to face drive electrode assembly 15 as shownin FIG. 4E. Some examples of adhesives that may be used in this bondingprocedure include, without limitation, epoxy resins, polyvinyl acetate,polyurethane and cyanoacrylate polymers.

FIG. 5 is a perspective view of a microfluidic channel device inaccordance with at least some embodiments herein. As shown in theexample, the array of drive electrode assemblies 15 may be patterned ina linear fashion upon the surface 14 of substrate 13. Opposite the driveelectrode assemblies 15 is reference electrode 12. The arrow representsthe introduction of a sample droplet of analytes into microfluidicchannel 18.

FIG. 6A is side cross-sectional schematic view of a planarmicrochromatograph incorporating a microfluidic channel device inaccordance with at least some embodiments herein. FIG. 6B is front/backcross-sectional schematic view of a planar microchromatographincorporating a microfluidic channel device in accordance with at leastsome embodiments herein. FIG. 6C is a top plan schematic view of aplanar microchromatograph incorporating a microfluidic channel device inaccordance with at least some embodiments herein.

Referring to FIGS. 6A, 6B and 6C, after a chemical reaction has beencarried out in a suitable microchemical reactor or other externalreactor, a sample of the reaction product containing analytes to beseparated may be transferred to microfluidic channel 18. The transfermay be performed by any suitable means, e.g., a micropipette, to theinlet port of microfluidic channel 18 and onto the first drive electrodeassembly 15 in the array. The mobile phase may be mixed with the productsample to produce sample droplet 60. Mixing of mobile phase and analytesmay be accomplished by electrowetting-induced mixing. Once mixing iscomplete, droplet 60 may be moved along drive electrode assemblies 15 byvoltage-induced motion, i.e., the electrowetting effect, as furtherdescribed below.

A motion of sample droplet 60 may be produced by static and/or periodicpotentials that are applied between reference electrode 12 and driveelectrode layer 20, hereinafter designated V_(j). A surface tensiondifferential on one side of droplet 60 can be produced by application ofvoltage V_(j) adjacent to the meniscus 61 of droplet 60 where motion isdesired. At the same time, a voltage potential towards the interior 62of droplet 60 may be maintained either at zero voltage or a voltagelower than V_(j).

The described voltages can be regulated relative to a potentialassociated with reference electrode 12. Successive application ofvoltage potentials on adjacent drive electrode layers 20 can result indroplet 60 being driven along the path defined by the drive electrodeassembly array.

According to some examples as shown in FIGS. 6A and 6B, sample droplet60 may be disposed on the first of drive electrode assemblies 15 in thearray. Droplet 60 may partially overlap an adjacent drive electrodeassembly 15 with intervening gap space 19 disposed between the first andthe second drive electrode assemblies 15 a, 15 b in the array. Voltagesmay be applied to the first and second drive electrode layers inassemblies 15 a, 15 b to spread at least a portion of droplet 60 acrossthe second electrode assembly 15 b. The voltage on the first driveelectrode assembly 15 a may then be deactivated or reduced to move thesample droplet 60 from the first drive electrode assembly 15 a to thesecond drive electrode assembly 15 b in the array and in like manner tosuccessive drive electrode assemblies in the array.

The surface tension responsible for producing the forces involved may bedictated by the following equation,

${\gamma (V)} = {{\gamma (0)} - {\frac{1}{2}{CV}^{2}}}$

Where γ(V) is the surface tension of a droplet at an electrode pad witha particular applied voltage V and γ(0) is the surface tension withoutan applied voltage. The capacitance per unit surface area betweendroplet 60 and underlying electrode 15 is denoted as C, which is acomposite value comprised of the capacitance of the insulator/adhesionlayer 21 and the capacitance of the stationary phase 22.

The surface tension without applied voltage, y(0), relies on one or morevariables including, without limitation, the polarity of the solvent inthe mobile phase, the concentration and species of the analytes, thecomposition and structure of stationary phase layer 22, and/or thepolarity of the surrounding medium in microfluidic channel 18. One ormore of these variables may be, in turn, determined by the nature of thesamples to be analyzed, the composition of the mobile and the stationaryphases, and the type of the separation desired. In some examples, theinitial surface tension {γ(0)'s} may be within the range of from about10 dyne/cm to about 100 dyne/cm and the voltages used in moving droplet60 along microfluidic channel 18 may be within the range of from about 5V to about 100 V.

The voltages on each of the drive electrodes layers 20 and/or referenceelectrode 12 may be controlled by an electrode selector as shown inFIG. 1. The electrode selector may be controlled by a processor as alsoshown in FIG. 1. In some embodiments, the microprocessor may be acomputer.

Various actuation voltage sequences may be used to control the sampledroplet speed (e.g., the rate of movement through microfluidic channel18) including the size and shape of the droplet across the driveelectrode assembly array. The actuation voltage may vary in magnitudeand pulse width. In some examples, droplet 60 could move at a speed ofabout 1 mm/hour to about 10 cm/hour. In some examples, droplet 60 couldhave a size of about 10 μm in diameter to about 5 mm in diameter. Insome examples, droplet 60 may have a volume of about 1 pl to about 1 mland a shape that is circle or long oval in cross-section. In someexamples, actuation voltages can vary from about 1 μV to about 10V andhave a pulse width of about 1 μsec to about 100 minutes. As droplet 60moves across the array of drive electrode assemblies 15, the analytesmay be eluted onto stationary phase layer 22. Sufficient time may beprovided to allow droplet 60 to dwell, or remain, upon surface 23 ofeach stationary phase layer 22 long enough so that the respectivefractions may diffuse from the mobile phase in the sample droplet anddiffuse within and bind to stationary phase layer 22. In some examples,the dwell time could be from about 0.01 sec to about 100 minutes.

In operation, droplet 60 may be introduced onto a drive electrodeassembly 15 in the array. An actuation of an adjacent drive electrodeassembly may be delayed until respective fractions diffuse from themobile phase of the droplet 60 and bind to stationary phase layer 22 ofthe drive electrode assembly. The time that a sample droplet passesthrough the microfluidic channel may be controlled by the time delaybetween the actuation voltages on adjacent drive electrodes assemblies.In addition, with the same mobile phase and stationary phase,chromatographic resolution may be adjusted by varying the dwelling timeof the droplet on the drive electrode assemblies. Thus, microfluidicdevices discussed herein provide great flexibility.

As previously indicated, reference electrode 12 may be fabricated from atranslucent conductor, e.g., of ITO glass. In addition, microfluidicchannel 18 may be reflective from its base due to the metal driveelectrode Therefore, various optical detection or spectroscopic analysismethods may be used to observe the separation of the sample droplet andanalyze various fractions immobilized within stationary phase layer 22.

FIG. 7 is a schematic illustration of an analytical system arrangedaccording to at least some embodiments described herein. An analyticalsystem 96 may include a light source 90, a spectrometer 92, microfluidicchannel device 10 and an advancing mechanism 94. In some examples, lightfrom a light source 90 in the UV (ultra-violet)-visible-near IR(infra-red) range of the spectrum may be incident upon drive electrodeassembly 15. The light may glance electrode assembly 15 at any angleentering and exiting from transparent reference electrode 12.Spectroscopy may be performed by a spectrometer 92 in accordance withany suitable technique, e.g., absorption spectroscopy or fluorescencespectroscopy both of which are described below.

Referring to FIGS. 1 and 7, absorption spectroscopy may be used todetect the fractionated analytes using a broadband light source from theUV to near-IR portions of the spectrum. In some examples that useabsorption spectroscopy, plate 11 may be constructed of a translucentmaterial and reference electrode 12 may be made of a translucentconductor such as ITO glass. A beam of input light, such as IR or UVgenerated by an IR or UV spectrometer, may be projected incident ontomicrofluidic channel 18. Correction for refraction from plate 11 andreference electrode 12 may be carried out by subtracting the intensityof the refracted light from the intensity of the incident light. Thelight intensity may be measured using photodiodes. After shining throughtransparent plate 11 and reference electrode 12, the broadbandinterrogation light may be projected onto stationary phase layer 22 ofdrive electrode assembly 15. The light reflected from the stationaryphase layer may refract and exit from microfluidic channel 18 tospectrometer 92 positioned to collect the reflected light. Usingspectrometer 92, a reference spectrum may be collected from stationaryphase layer 22. In some examples, spectrometer 92 does not includeeluted species on or within it. A sample spectrum may be collected fromthe stationary phase layer that contains eluted species. Usingmicroprocessor 26, the reference spectrum may be subtracted from thesample spectrum to produce reflectance absorption spectra, which maythen be used to identify the chemical species of the eluted analyte.

Fluorescence spectroscopy is similar to the absorption spectroscopymethod discussed above. Light 90 with a narrow band (or from a laser)ranging from UV wavelengths to near-IR wavelength may be used.Spectrometer 92 may be used to obtain the fluorescence spectra of theanalytes eluted onto stationary phase layer 22.

As shown in FIG. 7, drive electrode assembly 15 may be sequentiallyinterrogated by system 96 using spectrometer 92. In other examples,microfluidic chromatograph assembly 70 can be moved by an advancingmechanism 94 to sequentially place each drive electrode assembly 15under the spectrometer. For example, advancing mechanism 94 couldinclude a shuttle using a solenoid or servo-motor.

FIG. 8 is a block diagram illustrating an example computing device 400that is arranged to control a microfluidic device in accordance with atleast some embodiments of the present disclosure. In a very basicconfiguration 402, computing device 400 typically includes one or moreprocessors 404 and a system memory 406. A memory bus 408 may be used forcommunicating between processor 404 and system memory 406.

Depending on the desired configuration, processor 404 may be of any typeincluding but not limited to a microprocessor (μP), a microcontroller(μC), a digital signal processor (DSP), or any combination thereof.Processor 404 may include one more levels of caching, such as a levelone cache 410 and a level two cache 412, a processor core 414, andregisters 416. An example processor core 414 may include an arithmeticlogic unit (ALU), a floating point unit (FPU), a digital signalprocessing core (DSP Core), or any combination thereof. An examplememory controller 418 may also be used with processor 404, or in someimplementations memory controller 418 may be an internal part ofprocessor 404.

Depending on the desired configuration, system memory 406 may be of anytype including but not limited to volatile memory (such as RAM),non-volatile memory (such as ROM, flash memory, etc.) or any combinationthereof. System memory 406 may include an operating system 420, one ormore applications 422, and program data 424.

Application 422 may include a microfluidic device algorithm 426 that isarranged to perform the functions as described herein including thosedescribed previously with respect to FIGS. 1-7. Program data 424 mayinclude microfluidic device data 428 that may be useful for amicrofluidic device algorithm as is described herein. In someembodiments, application 422 may be arranged to operate with programdata 424 on operating system 420 such that control of a microfluidicdevice may be provided. This described basic configuration 402 isillustrated in FIG. 6 by those components within the inner dashed line.

Computing device 400 may have additional features or functionality, andadditional interfaces to facilitate communications between basicconfiguration 402 and any required devices and interfaces. For example,a bus/interface controller 430 may be used to facilitate communicationsbetween basic configuration 402 and one or more data storage devices 432via a storage interface bus 434. Data storage devices 432 may beremovable storage devices 436, non-removable storage devices 438, or acombination thereof. Examples of removable storage and non-removablestorage devices include magnetic disk devices such as flexible diskdrives and hard-disk drives (HDD), optical disk drives such as compactdisk (CD) drives or digital versatile disk (DVD) drives, solid statedrives (SSD), and tape drives to name a few. Example computer storagemedia may include volatile and non-volatile, removable and non-removablemedia implemented in any method or technology for storage ofinformation, such as computer readable instructions, data structures,program modules, or other data.

System memory 406, removable storage devices 436 and non-removablestorage devices 438 are examples of computer storage media. Computerstorage media includes, but is not limited to, RAM, ROM, EEPROM, flashmemory or other memory technology, CD-ROM, digital versatile disks (DVD)or other optical storage, magnetic cassettes, magnetic tape, magneticdisk storage or other magnetic storage devices, or any other mediumwhich may be used to store the desired information and which may beaccessed by computing device 400. Any such computer storage media may bepart of computing device 400.

Computing device 400 may also include an interface bus 440 forfacilitating communication from various interface devices (e.g., outputdevices 442, peripheral interfaces 444, and communication devices 446)to basic configuration 402 via bus/interface controller 430. Exampleoutput devices 442 include a graphics processing unit 448 and an audioprocessing unit 450, which may be configured to communicate to variousexternal devices such as a display or speakers via one or more A/V ports452. Example peripheral interfaces 444 include a serial interfacecontroller 454 or a parallel interface controller 456, which may beconfigured to communicate with external devices such as input devices(e.g., keyboard, mouse, pen, voice input device, touch input device,etc.) or other peripheral devices (e.g., printer, scanner, etc.) via oneor more I/O ports 458. An example communication device 446 includes anetwork controller 460, which may be arranged to facilitatecommunications with one or more other computing devices 462 over anetwork communication link via one or more communication ports 464.

The network communication link may be one example of a communicationmedia. Communication media may typically be embodied by computerreadable instructions, data structures, program modules, or other datain a modulated data signal, such as a carrier wave or other transportmechanism, and may include any information delivery media. A “modulateddata signal” may be a signal that has one or more of its characteristicsset or changed in such a manner as to encode information in the signal.By way of example, and not limitation, communication media may includewired media such as a wired network or direct-wired connection, andwireless media such as acoustic, radio frequency (RF), microwave,infrared (IR) and other wireless media. The term computer readable mediaas used herein may include both storage media and communication media.

Computing device 400 may be implemented as a portion of a small-formfactor portable (or mobile) electronic device such as a cell phone, apersonal data assistant (PDA), a personal media player device, awireless web-watch device, a personal headset device, an applicationspecific device, or a hybrid device that include any of the abovefunctions. Computing device 400 may also be implemented as a personalcomputer including both laptop computer and non-laptop computerconfigurations.

The present disclosure is not to be limited in terms of the particularembodiments described in this application, which are intended asillustrations of various aspects. Many modifications and variations canbe made without departing from its spirit and scope, as will be apparentto those skilled in the art. Functionally equivalent methods andapparatuses within the scope of the disclosure, in addition to thoseenumerated herein will be apparent to those skilled in the art from theforegoing descriptions. Such modifications and variations are intendedto fall within the scope of the appended claims. The present disclosureis to be limited only by the terms of the appended claims, along withthe full scope of equivalents to which such claims are entitled. It isto be understood that this disclosure is not limited to particularmethods, reagents, compounds compositions or biological systems, whichcan, of course, vary. It is also to be understood that the terminologyused herein is for the purpose of describing particular embodimentsonly, and is not intended to be limiting.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to embodiments containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should be interpreted to mean “at least one”or “one or more”); the same holds true for the use of definite articlesused to introduce claim recitations. In addition, even if a specificnumber of an introduced claim recitation is explicitly recited, thoseskilled in the art will recognize that such recitation should beinterpreted to mean at least the recited number (e.g., the barerecitation of “two recitations,” without other modifiers, means at leasttwo recitations, or two or more recitations). Furthermore, in thoseinstances where a convention analogous to “at least one of A, B, and C,etc.” is used, in general such a construction is intended in the senseone having skill in the art would understand the convention (e.g., “asystem having at least one of A, B, and C” would include but not belimited to systems that have A alone, B alone, C alone, A and Btogether, A and C together, B and C together, and/or A, B, and Ctogether, etc.). In those instances where a convention analogous to “atleast one of A, B, or C, etc.” is used, in general such a constructionis intended in the sense one having skill in the art would understandthe convention (e.g., “a system having at least one of A, B, or C” wouldinclude but not be limited to systems that have A alone, B alone, Calone, A and B together, A and C together, B and C together, and/or A,B, and C together, etc.). It will be further understood by those withinthe art that virtually any disjunctive word and/or phrase presenting twoor more alternative terms, whether in the description, claims, ordrawings, should be understood to contemplate the possibilities ofincluding one of the terms, either of the terms, or both terms. Forexample, the phrase “A or B” will be understood to include thepossibilities of “A” or “B” or “A and B.”

In addition, where features or aspects of the disclosure are describedin terms of Markush groups, those skilled in the art will recognize thatthe disclosure is also thereby described in terms of any individualmember or subgroup of members of the Markush group.

As will be understood by one skilled in the art, for any and allpurposes, such as in terms of providing a written description, allranges disclosed herein also encompass any and all possible subrangesand combinations of subranges thereof. Any listed range can be easilyrecognized as sufficiently describing and enabling the same range beingbroken down into at least equal halves, thirds, quarters, fifths,tenths, etc. As a non-limiting example, each range discussed herein canbe readily broken down into a lower third, middle third and upper third,etc. As will also be understood by one skilled in the art all languagesuch as “up to,” “at least,” “greater than,” “less than,” and the likeinclude the number recited and refer to ranges which can be subsequentlybroken down into subranges as discussed above. Finally, as will beunderstood by one skilled in the art, a range includes each individualmember. Thus, for example, a group having 1-3 cells refers to groupshaving 1, 2, or 3 cells. Similarly, a group having 1-5 cells refers togroups having 1, 2, 3, 4, or 5 cells, and so forth.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

What is claimed is:
 1. A method for analyzing a droplet, the methodcomprising: introducing the droplet containing an analyte to beseparated into an inlet of a microfluidic channel device, themicrofluidic channel device comprising an array of drive electrodeassemblies and a reference electrode, the drive electrodes assemblieseach comprising a drive electrode layer, a dielectric layer and astationary phase layer, the droplet being introduced onto a first driveelectrode assembly in the array, the droplet contacting the stationaryphase layer of the first drive electrode assembly and remaining incontact therewith for a sufficient period of time for the analyte topartition into, and be immobilized within, the stationary phase layer toproduce an analyte fraction and an analyte-depleted droplet; andadjusting a voltage potential across the first drive electrode assemblyand a successive drive electrode assembly that is substantially adjacentto the first drive electrode assembly effective to move theanalyte-depleted droplet to the successive drive electrode assembly inthe array.
 2. The method of claim 1, wherein the reference electrodeincludes an optically translucent material.
 3. The method of claim 2,further comprising analyzing the analyte fraction by spectroscopy. 4.The method of claim 2, further comprising analyzing the analyte fractionusing absorption spectroscopy.
 5. The method of claim 2, furthercomprising analyzing the analyte fraction using fluorescencespectroscopy.
 6. The method of claim 1, wherein the drive electrodelayer of each drive electrode assembly corresponds to one or more of asquare shaped electrode, a rectangular shaped electrode, a round shapedelectrode, and an elliptical shaped electrode.
 7. The method of claim 1,wherein each reference electrode facing a corresponding drive electrodeassembly corresponds to one or more of a square shaped electrode, arectangular shaped electrode, a round shaped electrode and an ellipticalshaped electrode.
 8. The method of claim 1, wherein a width of thereference electrode and each of the drive electrode assemblies is aboutas wide as the microfluidic channel.
 9. The method of claim 1, whereinthe microfluidic channel has a length of about 0.5 mm to about 50 mm, aheight of about 1 μm to about 5 mm, and a width of about 10 μm to about5 mm.
 10. The method of claim 1, wherein the reference electrode has adepth of about 100 nm to about 10 μm.
 11. The method of claim 1, whereinthe drive electrode assembly has a length of about 10 μm to about 1 mmand a width of about 10 μm to about 5 mm, the drive electrode layer hasa height of about 10 nm to about 1 μm, the dielectric layer has a heightof about 1 nm to about 1000 nm, the first stationary phase layer has aheight of about 1 μm to about 1 mm, and the second stationary phaselayer has a height of about 1 μm to about 1 mm.
 12. The method of claim1, wherein the channel is filled with water.
 13. The method of claim 1,wherein the microfluidic channel device includes a heater and the methodfurther comprises providing heat by the heater to the microfluidicchannel.
 14. A method for analyzing a droplet, the method comprising:introducing the droplet, wherein the droplet includes a first analyteand a second analyte, into an inlet of a microfluidic channel device,the microfluidic channel device comprising an array of drive electrodeassemblies and a reference electrode, the drive electrodes assemblieseach comprising a drive electrode layer, a dielectric layer and astationary phase layer, the droplet being introduced onto a first driveelectrode assembly in the array, the droplet contacting a firststationary phase layer of the first drive electrode assembly andremaining in contact therewith for a sufficient period of time for thefirst analyte to partition into, and be immobilized within, the firststationary phase layer to produce a first analyte fraction and a firstanalyte-depleted droplet; adjusting a voltage potential across the firstdrive electrode assembly and a second drive electrode assembly that issubstantially adjacent to the first drive electrode assembly effectiveto move the first analyte-depleted droplet to the second drive electrodeassembly in the array; introducing the first analyte depleted dropletonto the second drive electrode assembly in the array, the first analytedepleted droplet contacting a second stationary phase layer of thesecond drive electrode assembly and remaining in contact therewith for asufficient period of time for the second analyte to partition into, andbe immobilized within, the second stationary phase layer to produce asecond analyte fraction and a first and second analyte-depleted droplet;and adjusting a voltage potential across the second drive electrodeassembly and a successive drive electrode assembly that is substantiallyadjacent to the second drive electrode assembly effective to move thefirst and second analyte-depleted droplet to the successive driveelectrode assembly in the array.
 15. The method of claim 14, wherein thereference electrode is fabricated from an optically translucentmaterial.
 16. The method of claim 15, the method further comprisesanalyzing each analyte fraction by spectroscopy.
 17. The method of claim15, further comprising analyzing the analyte fraction using absorptionspectroscopy.
 18. The method of claim 15, further comprising analyzingthe analyte fraction using fluorescence spectroscopy.
 19. The method ofclaim 14, wherein the microfluidic channel device includes a heater andthe method further comprises providing heat by the heater to themicrofluidic channel.
 20. A method for analyzing a droplet, the methodcomprising: introducing the droplet, wherein the droplet includes afirst analyte and a second analyte, into an inlet of a microfluidicchannel device, the channel filled with water, the microfluidic channeldevice comprising an array of drive electrode assemblies and a referenceelectrode, the reference electrode fabricated from an opticallytranslucent material, the drive electrodes assemblies each comprising adrive electrode layer, a dielectric layer and a stationary phase layer,the droplet being introduced onto a first drive electrode assembly inthe array, the droplet contacting a first stationary phase layer of thefirst drive electrode assembly and remaining in contact therewith for asufficient period of time for the first analyte to partition into, andbe immobilized within, the first stationary phase layer to produce afirst analyte fraction and a first analyte-depleted droplet; adjusting avoltage potential across the first drive electrode assembly and a seconddrive electrode assembly that is substantially adjacent to the firstdrive electrode assembly effective to move the first analyte-depleteddroplet to the second drive electrode assembly in the array; introducingthe first analyte depleted droplet onto the second drive electrodeassembly in the array, the first analyte depleted droplet contacting asecond stationary phase layer of the second drive electrode assembly andremaining in contact therewith for a sufficient period of time for thesecond analyte to partition into, and be immobilized within, the secondstationary phase layer to produce a second analyte fraction and a firstand second analyte-depleted droplet; adjusting a voltage potentialacross the second drive electrode assembly and a successive driveelectrode assembly that is substantially adjacent to the second driveelectrode assembly effective to move the first and secondanalyte-depleted droplet to the successive drive electrode assembly inthe array; and analyzing each analyte fraction by absorptionspectroscopy.